Elastomeric ligature ring appliers proposed or available heretofore have been of two principal types, namely, the pliers-type and the tweezers-type. Both of these types are represented in Cusato U.S. Pat. No. 4,001,940, issued Jan. 11, 1977, the tweezers-type being shown in FIGS. 1 to 5, 5A and 6, and the pliers-type being shown in FIGS. 14 to 21.
Patents showing previous pliers-type of apparatus cited against the application resulting in the aforesaid U.S. Pat. No. 4,001,940 are Belgian Pat. No. 523,365 of October 1953, United Kingdom Pat. No. 764,150 of December 1956 and United Kingdom Pat. No. 921,015 of March 1963. Prior patents showing tweezers-type apparatus cited against the application resulting in U.S. Pat. No. 4,001,940 are Engelsman U.S. Pat. No. 955,955, issued Apr. 26, 1910, and Gardella U.S. Pat. No. 1,974,106, issued Sept. 18, 1934.
Patents issued later than U.S. Pat. No. 4,001,940 showing pliers-type of apparatus are Dragan U.S. Pat. No. 4,106,374, issued Aug. 15, 1978, and Frajdenrajch U.S. Pat. No. 4,310,305, issued Jan. 12, 1982.
The pliers-type of device includes jaws that are spring-pressed toward each other having tips that can be inserted into the aperture of an elastomeric ligature ring element after which the pliers handles can be pressed toward each other to spread the tips and thereby stretch and hold the ligature ring between the tips. U.S. Pat. No. 4,001,940 in FIGS. 17 and 18 provides a latch that can be engaged between the handle elements of the pliers to hold such elements in contracted position for maintaining the tips in spread condition to hold a ring stretched.
The tips of a tweezers-type of device are normally urged apart by the resiliency of the tweezers and the tips can be pressed together for engagement with a ligature ring and then released to spread and hold the ring. Such tweezers may have a latch to hold the legs of the tweezers apart for maintaining a ring in stretched condition, as shown in the Engelsman U.S. Pat. No. 955,955.
It is difficult to stretch and hold an elastomeric ring in stretched condition by manipulation of a pliers-type instrument when applying such a ring to the wings of an orthodontic bracket, and it is also difficult to manipulate latch mechanism for holding apart the jaws of such a pliers instrument and for releasing the jaws from a ligature ring. Moreover, such latch mechanism is intended to hold the pliers jaws spaced apart only a predetermined distance, whereas it may be desirable to stretch ligature rings different amounts depending on the type of bracket to which the ring is to be applied.
The tweezers-type of ring-holding instrument is difficult to hold firmly in the hand, and it is more difficult to hold such an instrument securely while manipulating latch mechanism to hold the legs of the tweezers in spaced relationship.